Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $76.33   8.232%   $82.6135   $82.61   $82.60   $82.60  
  Purchase #2 $52.38   6.752%   $55.9167   $55.92   $55.90   $55.90  
  Purchase #3 $122.58   13.844%   $139.55   $139.55   $139.55   $139.60  
  Purchase #4 $231.96   4.743%   $242.9619   $242.96   $242.95   $243.00  
  Purchase #5 $234.63   6.824%   $250.6412   $250.64   $250.65   $250.60  
  Purchase #6 $200.70   3.410%   $207.5439   $207.54   $207.55   $207.50  
  Purchase #7 $93.79   4.678%   $98.1775   $98.18   $98.20   $98.20  
  7 purchase totals = $1,012.37       $1,077.4047   $1,077.40   $1,077.40   $1,077.40